1. Field of the Invention
The present invention generally relates to a method for controlling data transmission in a radio communication system. In particular, the present invention relates to a method for controlling data transmission using response signals including additional control information that reflects received signal quality as well as response signals indicating whether the data transmission is made.
2. Background of the Related Art
Universal Mobile Telecommunications System (UMTS) is a third-generation mobile communication system that is more advanced than Global System for Mobile communications (GSM), which is the second-generation mobile communication system in Europe. A primary goal of this third-generation system is to provide users with multimedia mobile communication services based on GSM-core network and Wideband Code Division Multiple Access (WCDMA) air interface technology.
To standardize the IJMTS worldwide, the federation of nations or national standard establishment organizations like ETSJ of Europe, ARIB/TTC of Japan, TI of the United States, and TTA of Korea gathered together in December, 1998, and organized the Third Generation Partnership Project (hereinafter, it is abbreviated to 3GPP). Through this 3GPP, a more detailed specification for the UMTS as an IMT-2000 system has been regulated.
FIG. 1 illustrates a configuration of a standard interface protocol over a 3GPP wireless access network for interfacing a terminal and a network wirelessly in the air. Referring to FIG. 1, horizontally, the wireless access interface protocol is divided into a physical layer (PHY), a data link layer and a network layer. Vertically, the protocol includes a control plane for signaling and a user plane for transmitting data information. The user plane is a region where user traffic information like voice or IP packet transmission is transferred, and the control plane is a region where control information including an interface of the network or call maintenance and management is transferred.
The protocol layers in FIG. 1 can be divided into a first layer L1, a second layer L2, and a third layer L3, on the basis of 3 lower layers of the widely known 7-layer open systems interconnection (OSI) standard model in communication systems.
The first layer L1 acts as a physical layer (PHY) for the radio interface, and is connected to the medium access control (hereinafter, it is abbreviated to MAC) on the upper layer through transport channels. The first layer L1 primarily sends the data that was transmitted to the PHY through the transport channel to a receiving side using a variety of coding and modulation methods appropriate for the radio environment.
The second layer L2 acts as a data link layer, and lets many terminals share radio resources over the WCDMA network. The second layer L2 is divided into a MAC layer, a radio link control (hereinafter, it is abbreviated to RLC) layer, a packet data convergence protocol (hereinafter, it is abbreviated to PDCP) layer, and a broadcast/multicast control (hereinafter, it is abbreviated to BMC) layer.
The MAC layer transfers data using an appropriate mapping relation between logical channels and transport channels. Here, the logical channels are the ones connecting the upper layers to the MAC layers. Normally, a number of diverse logical channels are provided depending on the kinds of information to be transmitted.
The RLC layer constitutes an appropriate RLC protocol data unit (PDU) for transmission, matching with segmentation and concatenation of RLC service data unit (SDU) transported from upper layers, and conducts an automatic repeat request (ARQ) in charge of retransporting any lost RLC PDU.
The PDCP layer is disposed at an upper portion of the RLC layer, and makes the data that is transported through network protocols like IPv4 or IPv6 appropriate to be transported in the RLC layer.
The BMC layer transports the message that is transferred from a Cell Broadcast Center (CBS) through a radio interface. The primary function of the BMC is to schedule the cell broadcast message transported to terminals, and to transport the scheduled message. Most of time, the BMC layer transports the data through the RLC layer which operates in the no reply mode.
The RRC layer, which is the bottom layer of the third layer L3, is only defined on the control plane, and is in charge of controlling transport channels and physical channels associated with the setup, reset, and release of radio bearers.
The aforementioned WCDMA system targets 2 Mbps of transmission speed at the indoor and pico-cell environment, and 384 kbps in a general radio environment. However, as wireless internet is being widely used and the number of subscribers increase, more diverse services have been introduced to meet user needs, and in order to meet these needs transmission speed must be increased.
Consequently, the 3GPP is currently concentrating on a study for providing high transmission speeds by evolving (or developing) the WCDMA network. One representative system is known as the High Speed Downlink Packet Access (hereinafter, it is abbreviated to HSDPA). The WCDMA-based HSDPA system supports a maximum 10 Mbps for the downlink, and is expected to be able to shorten delay time and provide improved capacity. To provide improved transmission speed and capacity, the HSDPA system utilizes technologies like Link Adaptation (hereinafter, it is abbreviated to LA), Hybrid Automatic Repeat request (hereinafter, it is abbreviated to HARQ), Fast Cell Selection (hereinafter, it is abbreviated to FCS), or Multiple Input Multiple Output (hereinafter, it is abbreviated to MIMO) antenna.
The LA scheme uses a Modulation and Coding Scheme (hereinafter, it is abbreviated to MCS) that is suitable for channel status. More specifically, in case the channel status is good, an advanced modulation scheme like 16 QAM and 64 QAM is used, while if the channel status is not good, a low degree modulation scheme like QPSK is used.
The HARQ scheme, unlike the packet retransmission by the RLC layer, is a retransmission method with a totally new concept. It is linked to the physical layer and combines the retransmitted data with previously received data, thereby assuring a higher decoding success rate. According to this scheme, the untransported packets are not discarded but are stored, and they are decoded by combining with the retransmitted packet prior to the decoding step. Applying the LA, it becomes possible to increase the packet transmission speed to a great extent.
The FCS scheme is similar to soft handover techniques used in conventional systems. According to this scheme, although a terminal can receive data from a plurality of cells, only the data from a cell having the best channel status gets transmitted.
The MIMO antenna scheme makes it possible to increase the data transmission rate even in a channel environment which has a lot of scattering. This is accomplished by using a plurality of independent channels.
The HSDPA system tries to introduce a new technology while keeping its basis on the conventional WCDMA network as much as possible. However, slight modification is still needed to adapt new technologies. One example of this is found in a conventional base station (Node B) furnished with improved functions. More specifically, although the WCDMA network was mostly controlled by RNC, in the HSDPA system, the new technologies necessary for faster adaptation to different channel situations and for shortening delay time to the RNC are mostly controlled by the base station (Node B).
To this end, unlike the conventional WCDMA system, the base station (Node B) went through some modification to perform part of the MAC function, and the layer involved in this is called MAC-hs sublayer. The MAC-hs sublayer is disposed at an upper portion of the physical layer, and performs packet scheduling or carries out HARQ and LA functions. In addition, data transmission for the HSDPA system is performed using a transport channel called HS-DSCH (HSDPA Downlink Shared Channel), instead of a conventional transport channel. The HS-DSCH also has a short transmission time interval (TTI) (3 slot, 2 ms), which is different from the DSCH standard R'99/R'4 regulated by the WCDMA system, and supports diverse modulation code set (MCS) to obtain high data transmission rate.
For more reliable transmission, a hybrid ARQ (HARQ) developed from a combination of automatic repeat request (ARQ) with the channel coding was used. Through code division multiplexing (CDM), 4 users to the highest were supported at a time in this system.
As previously noted, for the HS-DSCH control information needs to be transmitted, and this information is usually transmitted through a shared control channel (HS-SCCH) introduced by the HSDPA standard. The control information transmitted through the HS-SCCH of the physical channel is divided into transport format and resource related information (TFRI), and HARQ related information. Particularly, the TFRI includes HS-DSCH transport channel set size, modulation method, coding rate, multicode number and so forth.
The HARQ related information includes block number and a redundancy version. Further, the UE identification (UE Id) can be transmitted to notify whom the information belongs. The UE Id related information, together with the TFRI and HARQ information, conducts a cyclic redundancy check (CRC) operation and transmits the CRC only. As for the HS-DSCH transmission, the 3GPP system supports a high-speed packet data service at a downlink.
In addition to the introduction of the packet data transmission described above, to get reliable data transmission, special technologies using error correction codes and requesting a retransmission by detecting errors have been developed. More specifically, the technology of using error correction codes utilizes redundancy bit called a self-correction code system, and detects/restores errors in the bit number within the redundancy bit. There are two ways to accomplish the error detection/correction: one is to use hamming code and the other is to transmit the same data more than twice to correct the errors, if they exist, after checking for any possible problems in the data. The technology of requesting a retransmission by detecting errors is called a retransmission feedback system. Again, there are two methods for the system: one is a simple information feedback and the other is an automatic repeat request (ARQ).
According to the information feedback method, information obtained from the receiving side is forwarded back to the transmitting side and the transmitting side checks if there is an error in the information. If there is, the information is retransmitted. According to the ARQ method, the receiving side examines whether there is an error in the transmitted data, and if there is, it notifies the presence of the error to the transmitting side, and the transmitting side retransmits the data with the error.
There are several kinds of ARQ methods, such as, Stop-and-Wait ARQ, continuous ARQ, and adaptive ARQ.
In the Stop-and Wait ARQ method, when the transmitting side transmits one data block to the receiving side, the receiving side first decides whether there is an error in the received block. If there is an error, the receiving side sends a retransmission request signal (hereinafter, it is referred to as negative acknowledgment, or NAK signal) to the transmitting side. If there is no error, the receiving side sends an acknowledgment signal (hereinafter, it is referred to as acknowledgment ACK signal) to the transmitting side. The transmitting side, on the other hand, transmits a next block upon receiving the ACK signal from the receiving side, and retransmits a corresponding block upon receiving the NAK signal or if there is no response until a certain amount of time lapses. Although the method seems to be easy and simple, its communication efficiency is not that good because every time the transmitting side transmits a block, it has to wait for a response from the receiving side no matter what.
The continuous ARQ method is further divided into Go-Back-N ARQ and Selective Repeat ARQ which are alternatives of the Stop-and-Wait ARQ. Here, the Go-Back-N ARQ method involves transmitting a plurality of data blocks, and especially when the NAK signal is sent from the receiving side, all blocks after the block that received the NAK signal are retransmitted. The selective repeat ARQ method involves retransmitting only the block that received the NAK signal.
The adaptive ARQ method makes it possible to change the length of the block dynamically to raise transmission efficiency. Here, the receiving side sends the error rate to the transmitting side, and allows the transmitting side adjust the length of the block before transmitting the block. In this manner, the adaptive ARQ has the best transmission efficiency. Actually, the ARQ method can be applied to the radio communication system as well.
Although many kinds of ARQ methods may be implemented in a radio communication system, basically the data receiving side should send an ACK or NAK signal to the transmitting side, designating the ACK or NAK signal as 1 bit signal. That is to say, when the receiving side transmits 1-bit ACK signal (for example, 1), the transmitting side regards the transmitted packet as having been properly received. However, when the receiving side transmits the NAK signal (for example, −1), the transmitting side concludes that the receiving side failed to receive a packet, so it retransmits the corresponding packet to the receiving side.
The HSDPA system described above made a regulation on the downlink data packet transmission of the Node B that user equipment should transmit 1-bit uplink response information (ACK/NAK) signal. In the radio communication system, the response information (ACK/NAK) signal the data receiving side transmits is designated in such manner that the data transmitting side can transmit the signal using high power and energy without any special protection like channel coding for faster interpretation. One example thereof is found in the HSDPA system, in which the user equipment transmits a 1-bit response information (ACK/NAK) signal that did not go through the channel coding to the uplink, and informs whether a corresponding data packet is successfully received or not.
FIG. 2 is a flow chart illustrating a conventional ARQ system. As shown in the drawing, in the case where packet data is received from the transmitting side (S111), the receiving side demodulates/decodes the packet data (S114). The receiving side then conducts a cyclic redundancy check (CRC) on the packet data, and confirms whether there is an error in the data (S117 and S120). When it turns out that there is no error generated, the receiving side generates an ACK signal and transmits the signal to the transmitting side (S123). In contrast, if there is an error in the data, the receiving side generates a negative acknowledgment (NAK) signal and transmits the signal to the transmitting side (S126). More specifically, the ACK signal or NAK signal is a response signal indicating the presence of an error in the data. Usually, +1 (ACK signal) or −1 (NAK signal) is mapped to be in correspondence to 1-bit information (0 or 1) and is transmitted to the transmitting side through an uplink. For example, the ACK signal +1 is mapped to 1, and the NAK signal −1 is mapped to 0, or vice versa. Therefore, such mapping relation should be preregulated.
The transmitting side discriminates whether the transmitted signal from the receiving side is the ACK signal (displayed as 1) or the NAK signal (displayed as 0), and sends the corresponding packet data to the signal back to the receiving side again. In case the information 0 is received from the receiving side, the transmitting side decides this as the NAK signal and retransmits (or returns) the same packet data. However, if the information 1 is received, it is regarded as the ACK signal, and the transmitting side transmits a new packet data to the receiving end.
To facilitate such communication between the transmitting side and the receiving side, binary information should be established to distinguish the ACK signal from the NAK signal. That is, when the receiving side sends the ACK signal, the information 1 is transmitted to the transmitting side, and at this time, binary information needs to be regulated to let the transmitting side recognize the information 1 as the ACK signal.
Also, in most radio packet transmission systems, the transmitting side and the receiving side operate on the basis that the response signal generation time is transmitted after a certain amount of time from the packet transmission time of the response object. When the transmitting side in the radio communication system transmits a packet, it naturally expects a response signal from the receiving side after a certain amount of time from the transmission time. Therefore, the packet transmitting side decides which signal, ACK or NAK, the response signal transmitted from the packet receiving side at the corresponding time belongs to, and performs the ARQ process thereon.
In summary, in the conventional ARQ system only the ACK signal or the NAK signal is transmitted to the transmitting side as the response signal associated with data transmission. While doing so, the transmitting side often has to transmit the data repeatedly to the receiving side because the situation of the channel from the receiving side to the transmitting side was not reflected on the signal. In addition, only 1 bit is assigned to transport the ACK signal or NAK signal in the conventional ARQ system, which means that even if the transmitting side managed to figure out the channel situation, there is no way to send this discovery to the transmitting side and let the channel situation be reflected on the signal